Abstract

The Nurra district in the Island of Sardinia
(Italy) has a Palaeozoic basement and covers, consisting
of Mesozoic carbonates, Cenozoic pyroclastic rocks and
Quaternary, mainly clastic, sediments. The faulting and
folding affecting the covers predominantly control the
geomorphology. The morphology of the southern part is
controlled by the Tertiary volcanic activity that generated
a stack of pyroclastic flows. Geological structures and
lithology exert the main control on recharge and groundwater
circulation, as well as its availability and quality.
The watershed divides do not fit the groundwater divide;
the latter is conditioned by open folds and by faults. The
Mesozoic folded carbonate sequences contain appreciable
amounts of groundwater, particularly where structural lows are generated by synclines and normal faults. The
regional groundwater flow has been defined. The investigated
groundwater shows relatively high TDS and
chloride concentrations which, along with other hydrogeochemical
evidence, rules out sea-water intrusion as the
cause of high salinity. The high chloride and sulphate
concentrations can be related to deep hydrothermal
circuits and to Triassic evaporites, respectively. The
source water chemistry has been modified by various
geochemical processes due to the groundwater–rock
interaction, including ion exchange with hydrothermal
minerals and clays, incongruent solution of dolomite, and
sulphate reduction.